1. Field of the Invention
The present invention relates to an apparatus and a method for performing a protocol that optimizes a transmission power in a network, and more particularly to an apparatus and a method for performing a protocol that optimizes transmission power in a point-to-multipoint communication (1:N) network. The present application is based on Korean Patent Application Nos. 2000-46810, 2000-66863, and 2001-10982, which are incorporated herein by reference.
2. Description of the Related Art
A wireless communication technology uses a radio wave for data transmission. Wireless communication apparatuses, which constitute a wireless communication system, are well known for mobility, portability, and simplicity. Further, due to the fact that the wireless communication system can transmit data regardless of the location of a user, the wireless communication system is used in wider range of the field. One example of the wireless communication system is a wireless Local Area Network (LAN), which makes up for the shortcomings of a wired LAN through an advanced wireless communication technology. Since the wireless LAN can extend to an area that was almost impossible for the wired LAN to reach, the wireless LAN has advantages of flexibility and installability.
Meanwhile, the wireless communication system uses centralized packet transmission and a distributed packet transmission. The centralized transmission method can be used only through a relay of a central node for the communication between a terminal node and a central node, or between a node to another node. Meanwhile, according to the distributed transmission method that uses an omnidirectional nature of the wireless system, the communication is carried out directly between the node to another node without requiring a relay of a separate central node. The distributed transmission method is particularly efficient in a network that is constituted by mobile terminals such as a Personal Ad-hoc Network, since the mobility can be guaranteed.
The mobile terminal used in the wireless network is supplied with power from a battery. Since the battery has a limited life span, there have been many suggestions to transmit data between the node at a minimum power, by exchanging transmission power information between the nodes. One example can be found in U.S. Pat. No. 5,450,616 and another in U.S. Pat. No. 5,465,398 (WO 95/10142).
According to U.S. Pat. No. 5,450,616, entitled “Method and Apparatus for Power Control in a Wireless LAN,” first, a sending node sends to a master a data packet containing transmission power information for an initial packet transmission in a wireless LAN. The master calculates a suggested value for the transmission power with the received power information and signal quality data. Then the master transmits the result of calculation to the slave. Accordingly, the sending node adjusts the packet transmission power according to such calculated suggestion value for the transmission power.
According to U.S. Pat. No. 5,465,398 (WO 98/10142), entitled “Automatic Power Level Control of a Packet Communication Link,” a target node compares a Received Signal Strength Indicator (RSSI) of a received signal with a stored minimum strength, and notifies a source node of a quantitative difference. The source node adjusts the transmission power so as the moving average over time of the received quantitative difference to satisfy a predetermined threshold. That is, the power level of the source node is adjusted according to the comparison result of the RSSI of the received signal and the minimum strength.
According to U.S. Pat. Nos. 5,450,616 and 5,465,398, transmission power can be adequately adjusted in the point-to-point communication between two nodes. However, in case of point-to-multipoint communication, which is usually expected in the wireless LAN, the transmission power cannot be optimized by the approaches suggested by the above two patents. This is because it is difficult to keep the power for all the wireless apparatuses in the communication at a minimum just by increasing or decreasing the transmission power. In other words, the approaches of the above two patents suggest that the transmission power be optimized with reference to the least optimal transmission status.
An example of the point-to-multipoint communication method for the wireless LAN is the Bluetooth technology. The Bluetooth technology is one of the wireless communication methods that does not require centralized management, and enables data transmission among the Bluetooth embedded apparatuses within a short-range distance without being connected by a cable. While the Bluetooth can provide point-to-point or point-to-multipoint connection, owing to absence of central control structure, it is hard to apply the Bluetooth technology in the network. One or more units that share the same channel are connected in a Piconet. Accordingly, in the Piconet, one of the Bluetooth embedded apparatuses serves as a master, while the other apparatuses serve as slaves. In the network constructed as the above, the master has to ensure that the communication to the slaves is performed at an adequate minimum transmission power and a constant adequate communication quality.